Vitamin K-dependent proteins contain 9 to 13 gamma-carboxyglutamic acid residues (Gla) in their amino terminal 45 residues. The Gla residues are produced by enzymes in the liver that utilize vitamin K to carboxylate the side chains of glutamic acid residues in protein precursors. Vitamin K-dependent proteins are involved in a number of biological processes, of which the most well described is blood coagulation (reviewed in Furie, B. and Furie, B. C., 1988, Cell, 53:505-518). Vitamin K-dependent proteins include protein Z, protein S, prothrombin, factor X, factor IX, protein C, factor VII and Gas6. The latter protein functions in cell growth regulation. Matsubara et al., 1996, Dev. Biol., 180:499-510. The Gla residues are needed for proper calcium binding and membrane interaction by these proteins. The membrane contact site of factor X is thought to reside within amino acid residues 1-37. Evans and Nelsestuen, 1996, Protein Sci., 5:suppl. 1, 163 Abs. Although the Gla-containing regions of the plasma proteins show a high degree of sequence homology, they have at least a 1000-fold range in membrane affinity. McDonald, J. F. et al., 1997, Biochemistry, 36:5120-5137.
Factor VII functions in the initial stage of blood clotting and may be a key element in forming blood clots. The inactive precursor, or zymogen, has low enzyme activity that is greatly increased by proteolytic cleavage at the R152I153 bond to form factor VIIa. This activation can be catalyzed by factor Xa as well as by VIIa-tissue factor, an integral membrane protein found in a number of cell types. Fiore, M. M., et al., 1994, J. Biol. Chem., 269:143-149. Activation by VIIa-tissue factor is referred to as autoactivation. It is implicated in both the activation (formation of factor VIIa from factor VII) and the subsequent activity of factor VIIa. The most important pathway for activation in vivo is not known. Factor VIIa can activate blood-clotting factors IX and X.
Tissue factor is expressed at high levels on the surface of some tumor cells. A role for tissue factor, and for factor VIIa, in tumor development and invasion of tissues is possible. Vrana, J. A. et al., Cancer Res., 56:5063-5070. Cell expression and action of tissue factor is also a major factor in toxic response to endotoxic shock. Dackiw, A. A. et al., 1996, Arch. Surg., 131:1273-1278.
Protein C is activated by thrombin in the presence of thrombomodulin, an integral membrane protein of endothelial cells. Esmon, N. L. et al., 1982, J. Biol. Chem., 257:859-864. Activated protein C (APC) degrades factors Va and VIIIa in combination with its cofactor, protein S. Resistance to APC is the most common form of inherited thrombosis disease. Dahlback, B., 1995, Blood, 85:607-614. Vitamin K inhibitors are commonly administered as a prophylaxis for thrombosis disease.
Vitamin K-dependent proteins are used to treat certain types of hemophilia. Hemophilia A is characterized by the absence of active factor VIII, factor VIIIa, or the presence of inhibitors to factor VIII. Hemophilia B is characterized by the absence of active factor IX, factor IXa. Factor VII deficiency, although rare, responds well to factor VII administration. Bauer, K. A., 1996, Haemostasis, 26:155-158, suppl. 1. Factor VIII replacement therapy is limited due to development of high-titer inhibitory factor VIII antibodies in some patients. Alternatively, factor VIIa can be used in the treatment of hemophilia A and B. Factor IXa and factor VIIIa activate factor X. Factor VIIa eliminates the need for factors IX and VIII by activating factor X directly, and can overcome the problems of factor IX and VIII deficiencies with few immunological consequences. Hedner et al., 1993, Transfus. Medi. Rev.,7:78-83; Nicolaisen, E. M. et al., 1996, Thromb. Haemost., 76:200-204. Effective levels of factor VIIa administration are often high (45 to 90 xcexcg/kg of body weight) and administration may need to be repeated every few hours. Shulmav, S. et al., 1996, Thromb. Haemost., 75:432436.
A soluble form of tissue factor (soluble tissue factor or sTF) that does not contain the membrane contact region has been found to be efficacious in treatment of hemophilia when co-administered with factor VIIa. See, for example, U.S. Pat. No. 5,504,064. In dogs, sTF was shown to reduce the amount of factor VIIa needed to treat hemophilia Membrane association by sTF-VIIa is entirely dependent on the membrane contact site of factor VII. This contrasts to normal tissue-factor VIIa complex, which is bound to the membrane through both tissue factor and VII (a).
It has been discovered that modifications within the xcex3-carboxyglutamic acid (GLA) domain of vitamin K-dependent polypeptides enhance their membrane binding affinities. Vitamin K-dependent polypeptides modified in such a manner have enhanced activity and may be used as anti-coagulants, pro-coagulants, or for other functions that utilize vitamin K-dependent proteins. For example, an improved factor VII molecule may provide several benefits by lowering the dosage of VIIa needed, reducing the relative frequency of administration and/or by providing qualitative changes that allow more effective treatment of deficiency states.
The invention features vitamin K-dependent polypeptides that include a modified GLA domain that enhances membrane-binding affinity of the polypeptide relative to a corresponding native vitamin K-dependent polypeptide. In some embodiments, activity of the vitamin K-dependent polypeptide also is enhanced. The modified GLA domain is from about amino acid 1 to about amino acid 45 and includes at least one amino acid substitution. For example, the at least one amino acid substitution can be at amino acids 2, 5, 9 11, 12, 29, 33, 34, 35, or 36, and combinations thereof. In particular, the at least one substitution can be at amino acids 11, 12, 29, 33 or 34, amino acids 2, 5, or 9, amino acids 11 or 12, amino acids 29 or 33, or amino acids 34, 35 or 36. The modified GLA domain may include an amino acid sequence, which, in the calcium saturated state, forms a tertiary structure having a cationic core with a halo of electronegative charge.
The vitamin K-dependent polypeptide may be, for example, protein C, activated protein C, factor IX, factor IXa or active-site modified factor IXa, factor VII, factor VIIa or active site modified factor VIIa, protein S, protein Z, or factor Xa or active-site modified Xa. The modified GLA domain of protein C or activated protein C may include substitution of a glycine residue at amino acid 12. Further substitutions in the GLA domain of protein C or activated protein C can include a glutamic acid residue at amino acid 33 and an aspartic acid residue at amino acid 34, a glutamine or glutamic acid residue at amino acid 11, a phenylalanine residue at amino acid 29, an aspartic or glutamic acid residue at amino acid 35, or a glutamic acid residue at amino acid 36. The modified GLA domain of factor VII, factor VIIa, and active site modified factor VIIa may include at least one amino acid substitution at amino acids 11 and 33. For example, a glutamine residue at amino acid 11 and a glutamic acid residue at amino acid 33 may be substituted. The modified GLA domain also can include an aspartic acid or glutamic acid residue at amino acid 35.
The modified GLA domain of protein S can include a substitution of an isoleucine, leucine, valine, or phenylalanine residue at amino acid 9. Further substitutions can include an aspartic acid or glutamic acid residue at amino acids 34 or 35. The modified GLA domain also can include a phenylalanine residue at amino acid 5, and further can include an amino acid substitution in the thrombin-sensitive loop, such as at amino acids 49, 60, or 70. The modified GLA domain of active-site modified Factor IXa can include a phenylalanine residue at amino acids 29 or 34, a phenylalanine, leucine, or isoleucine residue at amino acid 5, or an aspartic acid or glutamic acid residue at amino acids 34 or 35, and combination thereof.
The modified GLA domain of active-site modified Factor Xa can include a glutamine at amino acid 11 or an aspartic acid or glutamic acid residue at amino acid 35. The modified GLA domain of protein Z can include an asparagine or glutamine residue at amino acid 2 or an aspartic acid or glutamic acid residue at amino acids 34, 35, or 36.
The modified GLA domain of vitamin K-dependent polypeptides further can include an inactivated cleavage site. For example, factor VII can include an inactivated cleavage site, such as a substitution of an alanine residue at amino acid 152.
In another aspect, the invention features a vitamin K-dependent polypeptide that includes a modified GLA domain that enhances membrane binding affinity and activity of the polypeptide. The modified GLA domain of such a polypeptide includes at least one amino acid insertion at amino acid 4. The polypeptide can be factor VII or VIIa, protein C or activated protein C, factor X or Xa, or protein S. For example, the polypeptide can be factor VII or IIa, and can include the insertion of a tyrosine or glycine residue.
The invention also features a mammalian host cell that includes a vitamin K-dependent polypeptide. The polypeptide includes a modified GLA domain that enhances membrane-binding affinity of the polypeptide relative to a corresponding native vitamin K-dependent polypeptide. The modified GLA domain includes at least one amino acid substitution as described above. The vitamin K-dependent polypeptide may be, for example, factor VII or factor VIIa
The invention also relates to a pharmaceutical composition that includes a pharmaceutically acceptable carrier and an amount of a vitamin K-dependent polypeptide effective to inhibit clot formation in a mammal. The vitamin K-dependent polypeptide includes a modified GLA domain that enhances membrane-binding affinity of the polypeptide relative to a corresponding native vitamin K-dependent polypeptide. In some embodiments, activity of the polypeptide also is enhanced. The modified GLA domain includes at least one amino acid substitution. The vitamin K-dependent polypeptide may be, for example, protein C, activated protein C or active site modified factor VIIa, protein S, or active site modified factor IXa. The composition can include an anticoagulant agent (e.g. aspirin).
The invention also features a pharmaceutical composition that includes a pharmaceutically acceptable carrier and an amount of a vitamin K-dependent polypeptide effective to increase clot formation in a mammal. The vitamin K-dependent polypeptide includes a modified GLA domain that enhances membrane-binding affinity of the polypeptide relative to a corresponding native vitamin K-dependent polypeptide. The modified GLA domain includes at least one amino acid substitution. The vitamin K-dependent polypeptide may be, for example, factor VII, factor VIIa, factor IX or factor IXa. The pharmaceutical composition may also include soluble tissue factor.
A method of decreasing clot formation in a mammal is also described. The method includes administering an amount of a vitamin K-dependent polypeptide effective to decrease clot formation in the mammal. The vitamin K-dependent polypeptide includes a modified GLA domain that enhances membrane-binding affinity of the polypeptide relative to a corresponding native vitamin K-dependent polypeptide. In some embodiments, activity of the polypeptide also is enhanced. The modified GLA domain includes at least one amino acid substitution. The vitamin K-dependent polypeptide may be, for example, protein C, activated protein C or active site modified factor VIIa or factor IXa, or protein S.
The invention also features a method of increasing clot formation in a mammal. The method includes administering an amount of a vitamin K-dependent polypeptide effective to increase clot formation in the mammal. The vitamin K-dependent polypeptide includes a modified GLA domain that enhances membrane-binding affinity of the polypeptide relative to a corresponding native vitamin K-dependent polypeptide. The modified GLA domain includes at least one amino acid substitution. The vitamin K-dependent polypeptide may be, for example, factor VII, factor VIIa, factor IX or factor IXa
In another aspect, the invention features a method for identifying a vitamin K-dependent polypeptide having enhanced membrane binding affinity and activity. The method includes modifying the GLA domain of the polypeptide, wherein modifying includes substituting at least one amino acid in the GLA domain; monitoring membrane binding affinity and activity of the polypeptide having the modified GLA domain; and identifying the modified vitamin K-dependent polypeptide as having enhanced membrane binding affinity and activity if membrane binding affinity activity of the modified polypeptide is enhanced relative to a corresponding native vitamin K-dependent polypeptide. Suitable substitutions are described above. The polypeptide can increase clot formation or inhibit clot formation.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used to practice the invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.